The photogeology

The use of aerial photographs to obtain both qualitative and
quantitative geologic information is referred to as photogeology.
Aerial photographs are widely used today for identifying and mapping
landforms, drainage patterns, structural features such as faults and
folds, and rock or lithologic Units. Knowledge of the surface
attributes of a landscape also enables a geologist to infer or predict
subsurface characteristics and relationships. Airphotos are routinely
scanned for the following types of geologic studies:

compiling topographic and geologic maps

exploring for mineral, hydrocarbon, and groundwater deposits

identifying hazardous features or sites such as active earthquake
faults and areas prone to landslides

identifying and mapping landscape changes caused by a natural hazard
event such as a hurricane or earthquake

selecting potential construction sites for critically engineered
facilities such as dams or harbours.

The geologic interpretation of aerial photographs is
based on the fundamental recognition elements that include
shape, size, pattern, shadow, tone or colour, texture, association, and
site.
The quantity and quality of geologic information that can be
interpreted from aerial photographs is dependent upon the training and
experience of the Interpreter in geology and remote sensing.

The three-dimensional view of the terrain reveals important
topographic information that cannot be obtained by viewing single
photographs.

See for yourself, by gazing at the above photostereopair to see it in 3D.

Although oblique airphotos are often of value to the photogeologist,
most studies make use of vertical airphotos.

Most of the photographs used in photogeology are acquired
under relatively high solar illumination angles to ensure that ground
detail is not hidden by cast shadows.
When there is a need to enhance surface irregularities,
special purpose photographs are acquired with low sun angle
illumination. Whenever feasible, both high and low sun angle
photographs are obtained for a given study area.

Medium to large scale airphotos are best suited to the
detailed study of a localized area, whereas small scale airphotos,
such as those obtained from earth orbit, find their greatest utility
for regional surveys.

In photogeology, the convergence of information principle is
often employed, whereby an interpreter starts with small-scale
photographs for a synoptic view and gradually focuses upon a local or
target area by interpreting successively larger scale photographs.

Regardless of scale, however, it is important to remember that
ground observations (i.e., field geology) can't be replaced by
photogeology.